This invention relates to detection of electromagnetic radiation, and more particularly to a personal device for measuring ultraviolet radiation.
Ultraviolet (UV) radiation adversely affects human skin from birth to death. In addition to acute adverse effects such as sunburn, chronic exposure can cause premature aging of the skin, actinic keratoses, and basal carcinoma. With the reduction of the stratospheric ozone layer through anthropogenic influences, the problem of UV effects on the human skin may become even more severe.
Ultraviolet radiation can cause damage at the molecular level to organisms. The sensitivity of biological organisms increases with shorter wavelengths because of the higher photon energy. A sensitivity curve for reddening of the skin (erythema action spectra) has been defined by the Commission Internationale de l"" Éclairage (CIE).
Several types of ultraviolet B (UVB) detectors exist, including personal dosimeters for warning against harmful UVB rays. One example of a personal UV dosimeter is described by Rettberg and Horneck, 1998. In this dosimeter, spores of the bacterium bacillus subtilis are exposed to UV light. The film is then developed in a laboratory.
The most popular broadband UVB detectors are based on the Robertson-Berger spectrometer, which was developed in the 1970s. The principle of such a spectrometer is as follows. Incident light passes through an UV-transmitting quartz window. Then it passes through a UV-transmitting black glass (Schott UGS filter), which absorbs all the visible light except for a small fraction of the red light. The radiation transmitted through the first filter strikes a UV-B sensitive phosphorescence material (MgWO4). The phosphor absorbs the radiation and re-emits it as a visible green light. A second, green-glass filter (Corning 4010 filter) passes the fluorescent light from the phosphor while blocking the red light transmitted by the black glass. The intensity of the fluorescent light is measured by a solid state GaAsP photodiode, which has a peak response in the green and is not sensitive to red light. Small Robertson-Berger UV dosimeters systems weigh 200 grams or so and are expensive, making them too heavy and costly for a personal application.
One aspect of the invention is a dosimeter for measuring UV radiation. A UV filter has transmission characteristics that correspond to an erythema action curve, having two different decays in the high UV range. A photodiode receives UV radiation from the filter and outputs a current representing the amount of received radiation. An analog to digital converter converts the current into a digital signal. A logic circuit that converts the digital signal to an output value. An output means that indicates the output value to the user, and at least one input means permits the user to operate the dosimeter. The logic circuit can be a processor, so as to provide various programming and calculating features. The output and input devices can be as simple as an LED display and an on/off button, with additional features being possible as manufacturing choices.
An advantage of the invention is that no wavelength conversion by a phosphor is required. Instead, a photodiode behind a UV-transmissive filter is used. The photodiode, the filter, and all associated processing electronics may be implemented on a monolithic silicon wafer, thus providing an opto-electronic sensor on a chip.
The dosimeter provides real-time and quantitative data to prevent sunburn. It is compact and sufficiently inexpensive for consumer application, especially when mass-produced using semiconductor technology.